Despite their widespread use in high-pressure experiments, little is
known about the physical and chemical properties of carbon-containing
materials as they expand and cool to ambient conditions. As a result,
interpretation of experiments can rely on use of unconstrained models
with poor accuracy for the ensuing equation of state properties and
final chemical products. To this end, we use quantum simulations to
study the free expansion and cooling of carbon from metallic liquid
states achieved during shock compression. Expansions from three
different sets of shock conditions yielded of a variety of chain and
ring structures. We then quantify the relative amounts of graphite-like
and diamond-like particles formed during cooling and equilibration. We
observe that for all cases, graphene sheets are the majority product
formed with more extreme initial conditions producing increasingly
larger amounts of diamond particles. Our results can address key needs
for future meso-scale models of experiments, where knowledge of material
properties and chemical end products can have a pronounced effect on
interpreting experimental observables. (C) 2014 AIP Publishing LLC.